This is a quick and simple plugin I cooked up for a site of mine.  I needed a way to allow site authors to attach files and have them available for download without the author having to do anything other than attach.

To add a file simply add it as a post attachment just like you would with an image.  Instead of inserting into the post you just close the media window once it’s been uploaded.  You may want to take a look at the mime-config plugin if you’re going to be uploading non web file types.  WordPress tends to not like authors uploading some formats.

PNG icons are from http://www.famfamfam.com/lab/icons/silk/